Various integrated circuits allow internal circuits to operate with a voltage supplied from an external source. However, since various types of voltages are used in integrated circuits, it is difficult to supply all voltages used in the integrated circuits from an external source. Therefore, integrated circuits include a voltage generation circuits for internally generating a plurality of voltages based on the voltage received from the external source.
Most circuits in an internal integrated circuit, in addition to the voltage generation circuits, start a normal operation after an initialization operation for initializing some nodes inside the circuits to a predetermined level for a stable operation. However, when the levels of internal voltages are largely out of their target values immediately after the initialization operation of the voltage generation circuits, circuits operating with the internal voltages output from the voltage generation circuits are either abnormally operated or completely out of order.